In a Multiple-Input Multiple-Output (MIMO) relay channel, channel state information (CSI) at the source and the relay can improve the overall network throughput.
Power on/off beamforming with finite rate feedback has been proposed in W. Dai et al., “On the information rate of MIMO systems with finite rate channel state feedback using beamforming and power on/off strategy,” IEEE Trans. Info. Theory, vol. 55, no. 11, pp. 5032-5047, 2009, which considers point-to-point MIMO channels. For such a scheme, power allocation is not a problem because the transmitter uses constant power.
There have also been several studies which have considered resource allocation and achievable rate in MIMO relay arrangements (see, e.g., A. Host-Madsen et al., “Capacity bounds and power allocation for wireless relay channels,” IEEE Trans. Info. Theory, vol. 51, no. 6, pp. 2020-2040, 2005; Y. Liang et al., “Gaussian orthogonal relay channels: Optimal resource allocation and capacity,” IEEE Trans. Info. Theory, vol. 51, no. 9, pp. 3284-3289, 2005; L. Yingbin et al., “Resource allocation for wireless fading relay channels: Max-min solution,” IEEE Trans. Info. Theory, vol. 53, no. 10, pp. 3432-3453, 2007; and B. Wang et al., “On the capacity of MIMO relay channels,” IEEE Trans. Info. Theory, vol. 51, no. 1, pp. 29-43, 2005). All of these studies, however, assume perfect CSI at the source and/or at the relay. Unfortunately, the impractical assumption of perfect CSI makes the implementation of these approaches questionable in real communication systems.